ASSETS HELD FOR SALE - Schedule of Assets to be Sold (Details) - Electricity Generation Plant, Non-Nuclear - Public Service Company Of New Hampshire $ in Millions	Dec. 31, 2017 USD ($)
Regulatory Assets [Line Items]
Generation Assets to be Sold (Carrying Value)	$ 735.7
Less: Generation Assets Held for Sale:
Thermal Generation Assets (Fair Value less Cost to Sell)	(161.7)
Hydroelectric Generation (Carrying Value)	(57.9)
Total Generation Assets Held for Sale	(219.6)
Deferred Loss on Thermal Generation Asset Sale	$ 516.1